You'd have to check for others using the same drive as you. While streaming NFL I got 1073 from my 256GB 840 Pro (OS drive - you decide if the streaming would have resulted in a reduced score) and 1003 from my 128GB 840 Pro.

The lifespan of an SSD depends on the type of flash memory being used. It should last long enough though. For the average user, the limited number of writes isn't an issue.